1. Field of the Invention
The present invention relates to a piezo-electric type of pressure sensor, and, more specifically, to a piezo-electric type of pressure sensor in which a plurality of sensor elements arranged in a matrix detect a distribution of contact pressure, and to a pressure-detecting device employing such a piezo-electric type of pressure sensor.
2. Description of the Background Art
FIG. 7 shows a piezo-electric type of pressure-distribution sensor in which piezo-electric elements are arranged in a matrix for detecting a distribution of contact pressure. Such sensor is disclosed in Japanese Patent Laying Open No. 62-297735.
In FIG. 7, piezo-electric elements 1a, 1b, . . . are arranged in a matrix of 5 rows and 5 columns. Connection lines A.sub.1, A.sub.2, . . . disposed in each row are each electrically connected to upper electrodes of piezo-electric elements 1a, 1b, . . . in each row, and connection lines B.sub.1, B.sub.2, . . . disposed in each column are each electrically connected to lower electrodes of the piezo-electric elements 1a, 1b, . . . in each column.
In the structure of FIG. 7, one connecting line is provided in each row or each column, so that compared with a structure in which a connecting line is provided to each piezo-electric element, the number of connecting lines can be reduced to simplify a switching circuit for selecting a piezo-electric element to be used for a measurement.
If a pressure in a certain piezo-electric element 1a, for example, is to be measured, in the above conventional piezo-electric type of pressure-distribution sensor, a potential based on a distortion caused in the piezo-electric element 1a is measured through the connection lines A.sub.1 and B.sub.1.
On the other hand, in this structure, another closed circuit between connection lines A.sub.1 and B.sub.1 consisting of connection line A.sub.1 --piezo-electric element 1b--connection line B.sub.2 --piezo-electric element 1c--connection line A.sub.2 --piezo-electric element 1d--connection line B.sub.1 is formed at the same time. Accordingly, when measuring the potential in the piezo-electric element 1a, the potentials in such elements as 1b, 1c and 1d forming the above mentioned closed circuit affect the result of measurement.
Thus, in the above conventional structure, a pressure cannot be detected correctly due to interference of piezo-electric elements other than that to be measured.